01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Lower UTI in a man is a symptomatic bacterial infection confined clinically to the bladder. Dysuria, urgency, frequency and suprapubic discomfort support that localisation when there is no fever, flank pain or prostate syndrome. Sex alone does not prove systemic infection. However, a bladder diagnosis requires deliberate assessment because an obstructed urinary tract or infected prostate changes antibiotic choice, duration and the need for hospital care.
Culture is particularly useful in men: it identifies resistant organisms and provides a comparison if symptoms recur. A positive result without attributable symptoms is asymptomatic bacteriuria, which is usually not an indication for antibiotics. Interpret the history before the laboratory report. Urethral discharge, sexual exposure, colicky pain or longstanding voiding difficulty may point towards another diagnosis, sometimes coexisting with bacterial infection.
Key points
- Afebrile dysuria and frequency can represent localised male cystitis, but ask specifically about flank pain, perineal pain, retention and systemic illness.
- Obtain a midstream urine sample for culture before the first antibiotic dose, then give immediate treatment for a clinically diagnosed lower UTI.
- For reliably excluded prostate involvement and eGFR at least 45, nitrofurantoin modified release 100 mg orally twice daily for seven days is a NICE option.
- Fever, rigors, flank tenderness or circulatory deterioration require reassessment for systemic infection and an antibiotic that reaches the affected tissue.
- Review susceptibility promptly and reassess if symptoms worsen or fail to start improving within forty eight hours.
- Repeated infection, poor emptying or persistent haematuria calls for investigation of the underlying cause rather than repeated short empirical courses.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Ascending bacteria
Enteric organisms, particularly Escherichia coli, can ascend the urethra and cause symptomatic bladder infection. Prior antibiotic exposure and instrumentation alter the likely organisms and resistance pattern.
Impaired emptying
Bladder outlet obstruction, urethral disease or dysfunctional emptying can leave residual urine that favours bacterial persistence. These contributors become particularly relevant with recurrence or prominent voiding symptoms.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Urothelial inflammation
Bacterial interaction with the bladder lining provokes inflammation and sensory irritation, producing dysuria, urgency and frequency. Symptoms indicate a host response rather than merely the presence of bacteria.
- 2Urinary drug concentration
Some antibiotics achieve useful bladder urine concentrations while providing inadequate exposure in renal or prostate tissue. This explains why a susceptible urine isolate does not make every drug suitable for every urinary syndrome.
- 3Persistent bacterial reservoir
An infected prostate, stone or foreign material can maintain organisms despite transient improvement in bladder symptoms. Repeated episodes therefore require anatomical and microbiological comparison rather than duration changes alone.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Establish when dysuria, urgency and frequency began, whether symptoms are new, and whether suprapubic discomfort accompanies them. Record temperature and observations rather than relying on the patient describing himself as well.
Perineal or pelvic pain, painful ejaculation, fever and obstructive symptoms raise suspicion of prostatitis. When clinically indicated, a gentle rectal examination may support the diagnosis; vigorous prostate massage is inappropriate during an acute infection.
Rigors, flank pain, vomiting, hypotension, confusion or inability to pass urine demand urgent assessment for upper infection, sepsis or retention. A bladder-only drug cannot be relied upon for these syndromes.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Pretreatment midstream urine cultureFirst step - Why
- Identify the organism and preserve useful susceptibility information.
- Interpretation and limitations
- Collect before antibiotics when possible; in a symptomatic man send culture even if a dipstick is unconvincing. A resistant isolate should trigger treatment review, while mixed growth may require a better sample interpreted against symptoms.
- 02
Renal function and medication review - Why
- Check that the selected drug is suitable for this patient.
- Interpretation and limitations
- Obtain a recent credible eGFR when considering nitrofurantoin, particularly with older age or renal disease. Review allergy details, prior antibiotics and interacting medicines; an old normal creatinine does not establish current safety during acute illness.
- 03
Targeted bladder emptying assessment - Why
- Identify a contributor when voiding symptoms suggest poor emptying.
- Interpretation and limitations
- Assess stream, hesitancy, incomplete emptying and a palpable bladder. An indicated postvoid residual or specialist flow assessment answers a specific question; neither a single residual threshold nor routine imaging is required for every isolated infection.
- 04
First void urine STI testing - Why
- Investigate urethritis when the history suggests sexual transmission.
- Interpretation and limitations
- Use the appropriate first void specimen and local sexual health pathway for nucleic acid amplification testing. This is a different specimen and diagnostic purpose from the midstream bacterial culture, so one should not silently substitute for the other.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Urethritis
Dysuria with urethral discharge or a relevant sexual history suggests urethritis. Appropriate first void nucleic acid testing and sexual health assessment address a different infection mechanism from routine bacterial cystitis.
Acute prostatitis
Fever, perineal pain, painful ejaculation or a tender prostate suggest infection beyond the bladder. Retention and systemic deterioration can occur, changing urgency and antimicrobial requirements.
Urinary calculus
A stone can cause pain and haematuria with or without infection. Colic or recurrent urease-producing isolates should prompt consideration of imaging for a relevant structural cause.
Additional chapter-specific clues
Discharge or recent sexual exposure warrants an STI history and suitable testing. Consider stones, urethral pathology, bladder malignancy and noninfectious irritation when the symptom pattern or response does not fit cystitis.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked caseA localised infection resolvesFirst stepA thirty four year old has new dysuria and frequency without systemic symptoms.+
- 1He is afebrile with normal observations, no flank or perineal pain, no retention or discharge, and no concerning sexual exposure. His eGFR is 88, he has no drug allergy or G6PD deficiency, and assessment supports isolated bladder infection.
- 2A midstream culture is collected and he starts nitrofurantoin modified release 100 mg orally twice daily with food for seven days. He receives a clear plan to seek urgent help for fever, rigors, flank pain or difficulty passing urine.
- 3The culture grows nitrofurantoin-susceptible Escherichia coli. At forty eight hours he reports substantially less dysuria and normal oral intake; the result therefore supports completing the existing course rather than adding another antibiotic.
- 4Symptoms have resolved by the end of treatment. No repeat culture is ordered solely to prove sterilisation in this asymptomatic patient; recurrence would prompt a new culture and reassessment of prostate involvement or an emptying problem.
02ReassessmentWhen the bladder diagnosis changesSymptoms deteriorate or have not begun improving after forty eight hours.+
- 1Recheck observations, adherence, the actual formulation taken and the culture result. Ask again about pain location, fever and voiding because new information can change the presumed infection site.
- 2If systemic features or retention have developed, arrange urgent hospital assessment and use the relevant upper tract, prostatitis or sepsis pathway. Do not merely extend nitrofurantoin because the urine isolate appears susceptible.
- 3For persisting localised symptoms without instability, obtain an appropriate repeat sample when indicated and select treatment using susceptibility and the revised diagnosis. Consider urethritis and noninfectious causes if microbiology and symptoms disagree.
03Further investigationRecognise a recurrent contributorA second episode or longstanding voiding problem changes the clinical question.+
- 1Compare organisms and intervals between episodes, noting whether symptoms completely settled. Repeated growth of a similar organism may suggest persistence, although routine cultures do not prove identical strain identity.
- 2Arrange specialist assessment for recurrent infection in male urinary anatomy and investigate significant voiding dysfunction, renal impairment or suspected stones. Treat the current symptomatic episode while pursuing the cause.
- 3Reassess haematuria after infection settles and follow the appropriate suspected cancer pathway when indicated. Resolution of dysuria should not erase persistent visible bleeding or another concerning finding.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Nitrofurantoin modified release 100 mg capsules
Give 100 mg orally twice a day for seven days, with food or milk; this schedule is for the prolonged release formulation.Use the standard course only at eGFR at least 45 ml/min/1.73 m² and exclude pyelonephritis, systemic infection and suspected prostatitis. The 30–44 exception concerns selected short courses for resistant uncomplicated lower infection after benefit assessment. Do not give with G6PD deficiency, acute porphyria or hypersensitivity to nitrofurantoin, other nitrofurans or the formulation. Check urinary alkalinisers and magnesium trisilicate, which can reduce activity or absorption, and probenecid or sulfinpyrazone, which reduce renal excretion. Stop and assess new breathlessness, cough, jaundice or neuropathy; acute lung injury can occur in the first week.
Trimethoprim 50 mg per 5 ml oral suspension
An alternative adult lower UTI regimen is 200 mg, equivalent to 20 ml of this suspension, orally twice daily for seven days.For this suspension, an eGFR of 15–30 ml/min, including exactly 30, requires the usual dose for three days then half the dose; below 15 use half the usual dose from the outset. Thus half of the stated adult dose is 100 mg, or 10 ml, twice daily. Dialysis use requires infectious-disease and renal supervision. Exclude hypersensitivity, severe hepatic insufficiency, megaloblastic anaemia and other blood dyscrasias. Stop immediately for a severe rash with blistering, mucosal lesions or systemic illness; never restart after trimethoprim-associated SJS, TEN or DRESS. Monitor renal function and potassium, especially with ACE inhibitors, angiotensin receptor blockers or potassium-sparing drugs. Avoid unsafe methotrexate combinations; review warfarin, phenytoin and digoxin, and check blood counts during prolonged treatment. A seven-day bladder course does not treat established chronic prostatitis.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Ascending infection
Infection can extend to the kidney, producing flank pain, fever and systemic illness. New upper tract features warrant prompt reassessment even when bladder symptoms initially seemed straightforward.
Urinary retention
Inflammation can aggravate pre-existing outlet narrowing and precipitate retention. Inability to void or a painful distended bladder requires urgent assessment rather than another routine oral prescription.
Recurrent symptomatic infection
Persistence or reinfection can lead to repeated morbidity and antibiotic exposure. Comparing cultures and identifying contributory anatomy helps distinguish an unresolved source from separate new episodes.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Assign responsibility for checking the culture and contacting the patient if resistance or an unexpected organism changes management, including when symptoms have already partially improved.
- Explain that symptoms should begin improving within forty eight hours; worsening at any time requires review rather than waiting until the prescribed course finishes.
- Ask about oral intake, urine passage, new flank or perineal pain and adverse effects during reassessment, because these findings determine the next pathway more directly than an isolated dipstick.
- Document the final clinical response and investigate recurrence or persistent haematuria. Routine treatment of an incidental asymptomatic positive culture can create harm without addressing a clinical infection.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Localisation precedes duration
A seven day prescription can be appropriate for male bladder infection and inadequate for a prostate reservoir. The anatomy and syndrome explain the difference; antibiotic susceptibility alone does not establish tissue efficacy.
Negative nitrite limitations
A negative nitrite result does not safely exclude infection in a symptomatic man. Culture remains useful, and a sample collected after antibiotics can be falsely reassuring if bacterial growth has already been suppressed.
Resistance history matters
A recent isolate and recent antibiotic exposure may be more informative than a generic empirical preference. Record what was taken and when, including antibiotics prescribed elsewhere.
Avoid reflex instrumentation
One uncomplicated episode does not automatically require cystoscopy. Investigations should answer a question raised by recurrence, obstruction, stones, haematuria or another abnormal clinical finding.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling every positive urine culture a symptomatic UTI overlooks colonisation and exposes the patient to unnecessary antibiotic effects.
- 02
Choosing nitrofurantoin because a culture is susceptible while ignoring fever or perineal pain confuses laboratory activity with anatomical suitability.
- 03
Sending only an STI specimen or only a dipstick can leave a symptomatic male bacterial infection without the culture needed for treatment review.
- 04
Repeating empirical courses without recording symptom-free intervals, organisms and voiding symptoms delays recognition of a persistent prostate or obstructive source.